Constant duty, solenoid actuated vacuum control valves commonly are employed in air management systems of vehicle engines to direct, for example, either carburetor spark port vacuum or atmospheric pressure to the distributor's vacuum advance mechanism. Such vacuum valves typically operate at relatively high frequency and have employed a resilient conical tip needle valve element operatively actuated by a solenoid. To effect closure of one valve port, the resilient conical tip of the needle valve element is moved into sealing engagement with a conical valve seat which may be correspondingly tapered for full surface sealing contact.
Because the vacuum control valves typically operate at relatively high frequency, it has been found necessary to limit compression of the resilient conical tip upon closure thereof in order prevent the tip from being scrubbed away or forced through the valve seat opening or port by the action of the valve. For this purpose, the rigid body of the needle valve element has been provided with a stop surface adjacent the larger diameter end of the resilient conical tip. Upon closure of the valve seat port, the stop surface engages an opposed surface on the valve seat body after the resilient conical tip has engaged the correspondingly tapered valve seat and compressed sufficiently to effect a seal, and such engagement prevents further closing movement of the needle valve element thereby to preclude overcompression and scrubbing of the resilient conical tip. Typically, compression of the resilient conical tip is limited to a few thousandths of an inch.
Known vacuum control valves of the foregoing type, however, have drawbacks. In order to obtain desired sealing and compression of the resilient conical tip, the valve members must be formed and positioned within close tolerance. Otherwise, the valve may not fully close or too much compression of the resilient conical tip may result and cause scrubbing and hence failure of the resilient conical tip. In either case, the valve will not function properly.
In addition, the taper of the resilient conical tip must be precisely matched to the taper of the conical valve seat. Otherwise, undesirable variations in the operating voltage of the solenoid may occur in those valves in which the solenoid operates upon energization to unseat the resilient conical tip against differential pressure forces action thereon. If the taper mismatch is such that sealing is effected at the wide diameter end of the conical valve seat, a greater operating voltage would be required to unseat the resilient conical tip against the differential pressure normally acting to close the tip against the valve seat. Conversely, less operating voltage would be required if the taper mismatch is such that the seal is effected at the narrower or smaller diameter end of the conical valve seat.